[TUHS] One's complement (was: reviving a bit of WWB)
Ronald Natalie
ron at ronnatalie.com
Sat Sep 26 02:10:23 AEST 2020
The DECSystem20 (and the PDP-10 before) were 36 bit two's complement
machines. You had to go back to the PDP-1 if you want one's complement
in the DEC line. The CDCs and UNIVACs were the only ones that were
still kicking around in my era.
>>
>>Just to confirm, I pulled out my PDP-10 Hardware Reference Manual; Vol
>>I - CPU
>>(EK-10/20-HR-001), and it does indeed say (pg. 1-12): "The fixed-point
>>arithmetic instructions use 2's complement representations to do
>>binary
>>arithmetic." Selah.
>
>Back in school, we had our machine organization course. When we learned
>about 1's complement, the professor said "I've used a lot of machines
>that had this. You will likely never see one with it. There are no
>operational machines on campus with that."It stuck with me. We had a
>TOPS-20 machine... the odd turn of phrase was due to a professor that
>had a board of unknown origin hanging on the wall that was a rumored to
>be a CDC or similar... ah, the mid 80s...
Warner
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